getQueryObjectEXT(query, pname)

const ext = gl.getExtension("EXT_disjoint_timer_query");
const query = ext.createQueryEXT();
ext.beginQueryEXT(ext.TIME_ELAPSED_EXT, query);

// Draw
ext.endQueryEXT(ext.TIME_ELAPSED_EXT);

// At some point in the future, after returning control to the browser
const available = ext.getQueryObjectEXT(query, ext.QUERY_RESULT_AVAILABLE_EXT);
const disjoint = gl.getParameter(ext.GPU_DISJOINT_EXT);

if (available && !disjoint) {
  // See how much time the rendering of the object took in nanoseconds.
  const timeElapsed = ext.getQueryObjectEXT(query, ext.QUERY_RESULT_EXT);
}